You may have added a large scene. With the character selected, press F on your keyboard to zoom in on it.
As a way to compare size, the default grid squares are one meter across. So if your character is about two grid squares high, they are the correct size. So maybe you loaded a giant terrain?


Press Cntrl-G to show/hide the grid.
But if you do want to change the character scale, it is at the top of the Modify panel.